Drying Schedule for 8/4 Walnut

      Be careful when drying thick Walnut — drying too fast can damage the wood. January 14, 2013

Can someone tell me what schedule is used for 8/4 walnut and what the safe drying rate is? Also, how long does 8/4 walnut take to dry in kilns on average?

Forum Responses
From Gene Wengert, forum technical advisor:
Green or air dried? What type of kiln? Do you have samples and are weighing them, or do you use a meter? Do you have a copy of “Drying Hardwood Lumber”, as both schedule and rate would be there.

From the original questioner:
They are approximately 60% moisture content. I have six samples in the dry kiln. The first day I lost 6% on all samples (I thought that was ok as we had lots of snow that day that saturated the wood) but since then we have lost approximately 3% max on all samples.

From contributor K:
Be careful. I just wrecked a bunch of 8/4 walnut when I allowed 6% moisture drop even when it was already reading 33% MC. I just switched to Lignomat’s core probes so I wasn't used to the system and wasn't too careful. Max daily for walnut in 8/4 is 2.5% MC or such. I have lots of horrible end checks and possibly honeycomb now. I try to air dry most of my stock so as to avoid some of the worst defects, and as Gene has mentioned the defects occur over 40% MC.

From Gene Wengert, forum technical advisor:
Honeycomb (interior checks) in thick walnut is quite likely if the wood is dried too quickly, including end checks when drying too fast. Note that too fast drying can occur when air drying too - mainly above 30% MC. Under 30% MC, the risk of new damage drops to almost zero. The only safe way to dry thick walnut above 30% MC is using properly prepared weighing samples, as electronic techniques are not close enough.

From the original questioner:
We also use Lignomat control but when running the charge at the beginning we keep it on hold so we can control ourselves. Like I said we lost 6% the first day and then under 3% for the rest. We dropped the EMC and raised the temp only while watching the moisture lost per day. I believe that it may have happened in the steamer or air drying.

From Gene Wengert, forum technical advisor:
You can have a few small checks from improper (under 100% RH) steaming. They cause no problem unless subsequent drying is too fast or too hot. The proper kiln schedule is T3-D3 for 8/4, I believe. So, you cannot change the EMC much from the schedule values. You cannot under any circumstances raise the temperature over 110 F until under 30% MC. The safe drying rate is a maximum for any sample. It is not a target that you seek to maintain. You would therefore not drop the EMC to maintain a 3% daily rate. In practice, the average drying rate would be around 2% MC per day at higher MC’s. The rate is used to fine tune and not used as the primary control.

Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?

Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: Knowledge Base

  • KnowledgeBase: Lumber and Plywood

  • KnowledgeBase: Primary Processing

  • KnowledgeBase: Primary Processing: Kiln Operation

    Would you like to add information to this article? ... Click Here

    If you have a question regarding a Knowledge Base article, your best chance at uncovering an answer is to search the entire Knowledge Base for related articles or to post your question at the appropriate WOODWEB Forum. Before posting your message, be sure to
    review our Forum Guidelines.

    Questions entered in the Knowledge Base Article comment form will not generate responses! A list of WOODWEB Forums can be found at WOODWEB's Site Map.

    When you post your question at the Forum, be sure to include references to the Knowledge Base article that inspired your question. The more information you provide with your question, the better your chances are of receiving responses.

    Return to beginning of article.

    Refer a Friend || Read This Important Information || Site Map || Privacy Policy || Site User Agreement

    Letters, questions or comments? E-Mail us and let us know what you think. Be sure to review our Frequently Asked Questions page.

    Contact us to discuss advertising or to report problems with this site.

    To report a problem, send an e-mail to our Webmaster

    Copyright © 1996-2019 - WOODWEB ® Inc.
    All rights reserved. No part of this publication may be reproduced in any manner without permission of the Editor.
    Review WOODWEB's Copyright Policy.

    The editors, writers, and staff at WOODWEB try to promote safe practices. What is safe for one woodworker under certain conditions may not be safe for others in different circumstances. Readers should undertake the use of materials and methods discussed at WOODWEB after considerate evaluation, and at their own risk.

    WOODWEB, Inc.
    335 Bedell Road
    Montrose, PA 18801

    Contact WOODWEB

  • WOODWEB - the leading resource for professional woodworkers

      Home » Knowledge Base » Knowledge Base Article